Small scale fabrication has been dominated over the past 40 years by lithography techniques that employ radiation in the form or visible or ultraviolet light. However, these techniques are limited by the wavelengths of the light used and fabrication below 100 nm is problematic. Electron and ion beam lithography are alternative techniques capable of providing finer resolution but which typically use a serial scanning process that limits the speed of production. In addition, the use of masks for optical lithography and the required low pressure environmental control for e-beam lithography induces a high cost to modem fabrication processes.
Other techniques that have received attention because of their ability to fabricate structures with nanometer resolutions are nanoimprint lithography and scanning probe lithography. These techniques are distinguishable from the typical optical and electron based lithography discussed above in that these tools are proximal in nature and either contact, or are separated by a nanoscopic gap from, the substrate undergoing processing. Because the processing occurs at a proximal distance dispersion problems are reduced or eliminated, which enhances the maximum possible resolution.
Nanoimprint lithography employs a molded stamp structure with grooves formed therein so as to emboss, coat, or otherwise imprint a pattern on a target substrate. However, in repeated use, the stamp structure of the mold may be subject to erosion or soiling over time that can negatively impact the achievable resolution so that nanometer resolution patterning becomes impossible or inconsistent and high volume mass production becomes problematic.
Scanning probe lithography techniques employ devices with ultrafine tips to etch, coat, or otherwise treat a substrate so as to generate nanometer resolution patterns. However, scanning probe lithography is also a serial process and is therefore too time consuming to be employed in large scale fabrication.
Chapter 9 of Nanoelectronics and Information Technology (Ed. Rainer Waser, WILEY-VCH, 2003, pgs. 223-247) provides further background details of modem lithography approaches.
Within the past few years various approaches have been taken toward the use of large arrays of tips capable of field induced electron emission to accomplish lithographic procedures. Included in this group is the development of Massively Parallel Digital Electrostatic E-beam Array Lithography (DEAL) by Oak Ridge National Laboratory, a parallel electron beam machining tool and method as disclosed in U.S. Pat. No. 6,660,959, and a MEMS controlled parallel e-beam nanolithography tool as disclosed in U.S. Pat. No. 7,012,266. However, in order to control individual electron emitting tips in a large density array, wiring traditionally becomes a limiting factor and an effective parallel e-beam nanofabrication tool useful in mass production of a wide array of nanostructures, materials, or chemicals has yet to be developed.